We the people of the united states, in order to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defence, promote the general welfare, and secure the blessings of liberty to ourselves and our posterity, do ordain and establish this constitution for the united states of america.

this quote is important because it

concludes the declaration of independence
introduces and explains the purpose of the u. s. constitution
defines the purpose of the u. s. military
organizes the separate parts of the u. s. government